Ceramic die assembly

ABSTRACT

A CERAMIC DIE ASSEMBLY AND METHOD FOR MAKING SAME FOR METAL FORMING OPERATIONS SUCH AS DRAWING AND EXTRUDING INCLUDING A CERAMIC DIE BODY, A SUPPORTING RETAINER RING AND A LINING INTERPOSED BETWEEN THE DIE BODY AND THE RETAINER RING, WHERE THE PROPERTIES OF MODULUS OF ELASTICITY, COMPRESSIVE STRENGTH AND THE HARDNESS OF THE LINING ARE SUBSTANTIALLY GREATER THAN THOSE SIMILAR PROPERTIES OF THE RETAINER RING.

Oct. 5, 1971 CHARPENTIER 3,610,074

CERAMIC DIE ASSEMBLY "Filed March 21, 1969 INVENTORSZ ADELARD J. CHARPE/VT/ER 8 HARRY E. DEVERELL Attorney United States Patent Ofice 3,610,074 Patented Oct. 5, 1971 3,610,074 CERAMIC DIE ASSEMBLY Adelard J. Charpentier, New Castle, and Harry E. Deverell, Craigdell Gardens, Pa., assignors to Allegheny Ludlum Steel Corporation, Brackenridge, Pa.

Filed Mar. 21, 1969, Ser. No. 809,344 Int. Cl. B21k 5/20; B05b 7/20 US. Cl. 76-107 A 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Dies for extruding or drawing metals are subjected to extreme loading in both temperatures and pressures. At best, dies wear rather rapidly and must be replaced frequently. The die material conventionally may be combinations of tungsten and chromium steels or other alloys, perhaps including cobalt to increase the hardness of the material and create a more wear resistant surface. Ceramic dies have not been extensively used in ferrous extrusions, due in part to the expense incurred through the high rate of replacement of the retaining rings which support the die. Ceramic dies have good wear resistant characteristics, however, are relatively brittle and have low tensile strengths. Thus, it is necessary to 'keep them under compression or very low tensile stresses throughout their use. Failure to keep the ceramic die material under such proper loading results in die breakage. Moreover, the inside diameter of the retainer ring may be scored or gouged when the broken ceramic body is either removed for periodic replacement or is torn out during the drawing or extruding process.

Ceramic dies are installed in retaining rings by shrinkfitting in order to keep the ceramic body in compression. If the ceramic body chips or breaks, it may be removed from the retainer ring by any of several methods. Less desirable methods, including heating the ring and pressing the die out or cooling the die and then slipping the die out, consume excessive time and energy. The easiest method of passing the die out of the retainer ring is to press it out, however, this conventionally results in the scoring and gouging of the retainer ring due to the high hardness and abrasiveness of the die material. Subsequent use of the retainer ring is precluded until the interior diameter of the ring has been machined down smooth to remove the burrs and scoring so that in a subsequent interference fit, i.e. shrink-fitting, the die material will not be subjected to localized adverse stresses. It will be appreciated by those familiar with the art that repeated grinding and machining operations enlarge the inside diameter of the retainer ring, and eventually will deprive that ring of enough material to provide a sufiicient interference fit which will keep the die in proper compression.

SUMMARY OF THE INVENTION This invention relates to a ceramic die assembly and a method for making a ceramic die assembly for use in forming operations such as the drawing and extruding of metals including a ceramic die body and a supporting retainer means and a lining interposed between the die body and the retaining means and wherein the lining means has properties of modulus of elasticity, compressive strength, and hardness which are substantially higher than comparable properties of the retaining means.

It is therefore an object of our invention to provide a ceramic die and method for making same for forming operations wherein damage to the retaining means by breakup and pull-out of the die body is minimized.

A further object of our invention is to provide a ceramic die and method for making same for forming operations wherein a worn die body may be pressed out without damaging the retainer means.

A still further object of my invention is to provide a ceramic die and method for making same for forming operations wherein outsized retainer rings may be reclaimed by additional lining.

These and other objects of my invention will become apparent upon reading the description of the preferred embodiment which follows.

DESCRIPTION OF THE DRAWINGS The figure is an exploded view of the ceramic die assembly in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the figure, reference numeral 2 indicates a retaining ring of a generally cylindrical shape having an inside diameter 4. Disposed within the diameter 4 is liner 6, also cylindrical in shape and fitting closely thereinto. A ceramic die body 8 is then fit within the inside diameter 4 of retaining ring 2, having liner 6 disposed between the die 8 and the ring 2.

The embodiment described is a ceramic die assembly for extruding stainless steel tubing utilizing a ceramic die body 8 fit in either a steel or cermet retaining ring 2. It is to be noted, however, that the principles embodied herein may be applied equally well in non-ferrous drawing and extruding and may be of other mounting configurations. The material selected as a liner 6 for retainer ring 2 is chosen according to four characteristic requirements: (1) by hardness relative to both the retainer ring and the die to prevent gouging and scoring of the inside diameter 4 of the retaining ring 2 and the lining 6; (2) good adherence to the retainer ring to make sure that the liner will maintain itself within the inside diameter 4 of the retainer ring and thus be suitable for multiple refit of additional die bodies 8; (3) moderately high elastic modulus both so that deformation will not be concentrated in the liner robbing the liner of its support and the liner will resume its initial internal diameter upon the removal of the worn die and prior to the replacement with a serviceable one; (4) moderately high compressive strength to make sure that the material will not fracture under heavy loading of the die and thus score or gouge the inside diameter of the retaining ring. The retainer ring in the example is AISI H-13 Steel with hardness of R.,5052 and with an outside diameter of 5.250 and an inside diameter of 2.440". The inside diameter of the ring was badly scored by previous dies and too large for a sufficient interference fit with another die. The inside diameter was grit blasted with G-16 steel grit at to lbs. pressure removing burrs and gouges preparing it for a lining 6. In so doing the inside diameter of the ring was increased to 2.449". A tungsten carbide coating was placed on the inside diameter 4 of the ring 2 in order to build up the inside diameter to a useable size. The tungsten carbide was in powder form of -200 mesh (by Ro-Tap screen analysis) and containing a blend of approximately 7% cobalt. The carbide coating was placed on the inside diameter 4 by means of a plasma spray coating process utilizing a nitrogen gas at 50 lbs. pressure and flow rate of 100 cubic feet per hour. The secondary plasma gas was hydrogen also at 50 lbs. pressure with a flow rate of cubic feet per hour. The powder control rate was 30 to 50 lbs/hr. and the electrical power consumed was 400 amps. The coating thickness of the tungsten carbide was put on to a depth of 0.007 or a total of 0.0l4" on the diameter. The tungsten carbide liner 6 was then ground removing 0.0005" in order to obtain the desired inside diameter to the liner, i.e. 2.440". The ring 2 was then interference fit with a ceramic die by heating the ring up to 950 F. and dropping the ceramic ring into the inside diameter and allowing the retainer ring to cool and shrink to the appropriate fit. After the retainer ring and die in the example were returned to service, twelve extrusions were pushed through the die producing 620 ft. of 1" stainless steel pipe. The die was then taken out of service because it had worn to a size which exceeded tolerances. -It is to be noted that the die did not go into tension and break out. When thering was taken out of service the die 8 was pressed out of the ring, coming out in one whole piece. Previous to our invention, when ceramic dies were pushed out of retainer rings wherein they had been interference fit, the die break up, thus scoring and gouging the inside diameter of the ring. In the instant example the inside diameter of the ring was smooth following the press out and found, when measured, to be the same size as before fitting with a die. The liner 6 had not chipped, spalled or worn and required no additional preparation prior to fitting a second die. The press out of the die interference fit with a liner 6 of our invention required a load of 6,000 lbs. Previous to our invention and without the liner, press out loadings were normally 10,000 to 35,000 lbs. additionally encouraging the break up, scoring and gouging of the inside diameter of the ring. The high modulus of elasticity and the high compressive strength of the liner of our invention insures that the ceramic die, when interference fit within the ring, remains in compression thereby suppressing the tendency of the die to break up. The high hardness of the lining prevents gouging and scoring of the inside diameter of the retaining ring when the die is pressed out by the hard ceramic die. Further, the juxtaposition of the relatively equal but high hardness surfaces of the retaining ring and the liner exhibits a relatively low coeflicient of sliding friction between those two surfaces, thus reducing the force requirements to remove a worn die from the retainer ring. The combination of lower force and an easier exit allows the expended die to be removed whole, thus further limit ing the destruction and wear of the inside diameter of the retainer ring.

Though the liner 6 described above was of a coating of tungsten carbide laid on the inside diameter 4 of the retainer ring 2, this is considered exemplary rather than exclusionary in that the liner could also consist of a sleeve of similar material also interference fit within the ring between the die and the ring. An alternative embodiment may include lining means that is formed in situ such as by case hardening the surface of the inside diameter of the retainer ring.

We claim:

1. A method of making a ceramic die assembly suitable for use in forming operations such as drawing or extruding, which comprises the steps of: providing a ceramic die body and means to support said ceramic body in compression; providing said support means with a lining, said lining having a modulus of elasticity, a compressive strength and a hardness substantially greater than the material from which said support means is constructed; and subsequently assembling said ceramic body within said lined support means, said lining being between said ceramic body and said support means.

2. A method according to claim 1 wherein said lining is provided by coating said support means with a material which forms said lining.

3. A method according to claim 2 wherein said support means is coated with powdered tungsten carbide.

4. A method according to claim 2 wherein said lining material is heated to bond same to said support means.

5. A method according to claim 2 wherein said lining material is plasma spray coated on said support means.

6. A method according to claim 1 wherein said lined support means and said ceramic body are assembled by shrink fitting said lined support means about said ceramic body.

7. A method according to claim 1 wherein said support means is a material from the group consisting of steel and cermet.

8. A method according to claim 7 wherein said lining is tungsten carbide.

References Cited UNITED STATES PATENTS 3,248,788 5/1966 Goldstein 117-1052 2,882,759 4/ 1959 Altwicker 76-107 A 3,195,374 7/1965 Coffin 76-107 2,736,670 2/1956 'Griffiths 76-107 X 2,232,417 2/1941 Unokel 76-107 A 2,964,420 12/1960 Poorman 117l05.2 3,013,657 12/1961 Altwicker 76-107 A 3,395,030 7/1968 Dittrich 1l7-l05.2

FOREIGN PATENTS 584,016 1/ 1947 Great Britain 76-107 A OTHER REFERENCES The Metco Flame Spraying Processes (1960).

CHARLES W. LANHAM, Primary Examiner R. M. ROGERS, Assistant Examiner U.S. Cl. X.R. 117-1052 

